Interactions of retrotransposons with the host genome: the case of the gypsy element of Drosophila.

Insertion of the gypsy retrotransposon into various Drosophila genes results in mutant phenotypes that can be altered by second site mutations in a variety of modifier loci. One of these loci is the suppressor of Hairy-wing, which encodes a DNA-binding protein that binds to specific sequences of the gypsy element to regulate its expression. Interactions between the su(Hw) protein and transcription factors responsible for expression of the mutant genes are the primary cause of gypsy-induced phenotypes. Gypsy also appears to mediate effects in trans between copies of a gene located on homologous chromosomes. This interchromosomal communication allows transcriptional enhancers located in one chromosome to interact with their target promoter located on the other homolog.